Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 121739

Area Forecast Discussion
National Weather Service Lincoln IL
1139 AM CST Tue Dec 12 2017

Issued at 1029 AM CST Tue Dec 12 2017

Cold and breezy conditions will take place today behind
yesterday`s cold front. The breeziest areas will be east of I-55
as surface high pressure ridging and associated weaker pressure
gradients are beginning to build into western IL and will spread
east during the day. Mostly sunny conditions can be expected due
to the high pressure, however a few cloud bands can be expected
at times due to lingering cyclonic flow aloft. Cold advection will
cause temperatures to rise only a few degrees from current
temperatures, only reaching the mid to upper 20s along I-74 to the
low 30s from Springfield to Lawrenceville southward. Have made
minor updates for short term wind and cloud trends, but otherwise
forecast is mainly on track for today.


.SHORT TERM...(Today and tonight)
ISSUED AT 320 AM CST Tue Dec 12 2017
For the most part, not a lot of changes in this run. Northwesterly
flow continues, bringing a series of shortwaves into the Midwest.
The better chances for precipitation remain to the north and
central Illinois gets some slight chances and flurries/sprinkles
at best for most of the forecast. Cooler air moving into the
region right now going to keep much of the area below freezing
today. Teens and 20s filtering into central IL this morning will
throw the diurnal trend off a bit, with some areas, particularly
in the southern half of ILX forecast area, hitting their max temps
for the day this morning. Not a lot of variation in the temps
throughout the day. Blustery conditions this morning may ease a
bit later, but winds to 15-20 mph will keep the wind chills in
the single digits and low teens this morning... teens and low 20s
this afternoon. Tonights lows will be in the teens and lower
20s...with winds easing a bit.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 320 AM CST Tue Dec 12 2017
Next waves comes through the region on Wednesday and Friday, with
deeper cold air moving into place Wednesday night through Friday.
Wednesday will be slightly warmer than today until the reinforcing
shot of cold air moves in. Front will bring slight chances for the
northeast in the form of rain in the afternoon, ending quickly.
Forecast gets another shot of cold air to wrap up the week, and a
weak chance for precip again on Friday. Major systems not really
in the model forecasts for Central IL. A bit of a pattern shift in
the wake of Friday, with flow becoming almost zonal aloft as temps
are allowed to warm a few degrees. A larger wave dives into the
western half of the CONUS Friday, and at this point, the models
diverge in the progression. Models vary between cutting off the
system to the SW...and moving it through as an open wave. For now
the forecast over the weekend is relatively mild temperature
wise...and slight chances for precip on Sunday. However,
confidence is low in the behavior of that wave after the pattern
shift, as ensembles diverge quite a bit.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1139 AM CST Tue Dec 12 2017

High pressure moving into central IL will promote decreasing winds
until around 06Z then another low approaching from the NW will
bring increasing S-SW surface winds and winds aloft through the
latter portions of the TAF forecast period. As a result of strong
SW winds aloft have included low level wind shear from 10-15Z at
KSPI-KBMI-KPIA due to 45 kt flow at 1500 ft AGL. Surface winds NW
12-17 kts with gusts over 20 kts through afternoon today,
decreasing to light and variable for several hours from evening
into early morning. S-SW winds then 10-12 kts by 12Z, increasing
to 15-20 kts with gusts 25-30 kts by 18Z.




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